The present invention relates generally to power amplifiers and, more particularly, to increasing the efficiency of power amplifiers.
Power amplifiers are essential components in many electronic devices. For example, in cellular devices, such as cellular telephones, a transmitter power amplifier converts power from a direct current (DC) power source to radio frequency (RF) power for transmitting RF signals to other devices. Such RF power amplifiers operate at maximum efficiency, in relation to DC to RF power, when operating at or near their saturated power output level.
Many cellular applications use saturated transmitters, such as devices operating in accordance with the U.S. advanced mobile phone system (AMPS) analog frequency modulation (FM) system or the global system for mobile communications (GSM) digital cellular system. Cellular devices using linear modulation schemes, such as devices operating in accordance with the U.S. digital system known as D-AMPS or IS136, do not use saturated amplifiers and therefore, battery life or xe2x80x9ctalk timexe2x80x9d is not as high as when saturated amplifiers are used. Saturated amplifiers, however, have been employed to amplify linear signals.
The present invention is directed to harmonic matching circuits for saturated amplifiers. Such harmonic circuits may also be useful in linear amplifier applications, such as IS136/D-AMPS.
According to one implementation of the present invention as embodied and broadly described herein, a transmitter power amplifier that converts power from a DC supply to RF in a load resistance is provided. The transmitter power amplifier includes an amplifier that includes at least one active output device, where the amplifier has an output capacitance. The transmitter power amplifier also includes a harmonic terminating and impedance matching network that includes a number of sections coupled between the amplifier and the load resistance. A first section nearest the amplifier creates an impedance at the active output device, where the impedance is resonant with the output capacitance at a highest harmonic frequency and compensates for the output capacitance to produce a high impedance at the highest harmonic frequency. A second section nearest the load resistance creates an impedance at the active output device, where the impedance resonates with the output capacitance at a lowest harmonic frequency and compensates for the output capacitance to produce a high impedance at the lowest harmonic frequency.
In another implementation consistent with the present invention, a method is provided in a mobile terminal that includes an amplifier having an output capacitance. The method includes converting power from a DC power supply to RF power, via the amplifier. The method also includes creating a first impedance at an output of the amplifier, the first impedance resonating with the output capacitance at a first harmonic frequency and compensating for the output capacitance to produce a high impedance at the first harmonic frequency. The method further includes creating a second impedance at the output of the amplifier, the second impedance resonating with the output capacitance of the amplifier at a second harmonic frequency and compensating for the output capacitance to produce a high impedance at the second harmonic frequency.
In a further implementation consistent with the present invention, a class-F amplifier is provided. The amplifier includes an input that receives a sinusoidal drive signal. The amplifier also includes at least one active output device that receives the sinusoidal drive signal, where the active output device is forward-biased with a predetermined current. The amplifier further includes a harmonic network coupled to the active output device, where the harmonic network terminates odd harmonic frequencies to generate a substantially square wave output voltage signal waveform and a sinusoidal output current waveform.